The long term objective of this investigation is to understand how neural systems are constructed; that is, what are the mechanisms and rules which read out information available either in the genes or in the environment into neurons of appropriate number, type, and connectivity? The immediate objective of this project period is to provide an accurate description of what actually happens in construction of a neural subsystem which performs a specific task during a specific period of an animal's life. This involves answers to the following questions: When are the neurons which compose the system built? How is their mature structure established? How do the cells develop physiologically? When and how is functional connectivity within the system produced? What is the role of use or of feedback in achievement of the correct adult output? A careful description of what does happen in construction of such a system should provide strong evidence about the mechanisms and rules of construction, and should eliminate a number of hypotheses. BIBLIOGRAPHIC REFERENCES: Bentley, D. (1976) Genetic analysis of the nervous system. In: Fentress, J. C. (Ed.) SIMPLER NETWORKS: AN APPROACH TO PATTERNED BEHAVIOR AND ITS FOUNDATIONS. Sinauer, N. Y.